In addition to a hydraulic braking system, some hybrid vehicles and electric vehicles with a motor-generator are also equipped with a regenerative braking system. The regenerative braking system uses a motor-generator as a generator when a driver releases his foot from an accelerator pedal or when a brake pedal is depressed, and decelerates a vehicle by transforming kinetic energy into electrical energy (regenerative braking). The electrical power which is then generated is stored in a battery or capacitor. Tokkai Hei 6-219259 published by the Japanese Patent Office in 1994 disloses an electric vehicle equipped with such a regenerative braking system.
While the motor-generator is functioning as a generator, the braking force due to the hydraulic pressure brake is reduced according to the magnitude of the regenerative braking force, i.e., the amount of power generated by the motor-generator. It is therefore ensured that the total braking force does not vary before and after regenerative braking. This is known as regeneration co-operative control.